The present invention relates to an optical waveguide which is required of an optical integrated circuit to be used in an optical communication or optical processing field and to a process for fabricating the optical waveguide.
The optical waveguide is constructed of a core, which is overlaid on a substrate material for optical waveguidance, and a clad having a lower refractive index than that of the core portion. No matter what construction the optical waveguide might have, therefore, there are required two or more kinds of transparent materials of different refractive indexes, both or all of which have to be thin films. Moreover, the differences in the refractive index between or among those transparent materials is within 5 to 6% at most in most cases. As the materials for the optical waveguide, a number of materials such as semiconductors, ferroelectrics, glass or organic substances are reported in the prior art, and a coxbination of the materials having a suitable difference in refractive indexes is selected in accordance with this object. However, the actually applicable combination of the thin film materials is seriously restricted consideration is given to the construction, the difference in the refractive index between or among the respective portions and the fabricating process of the optical waveguide. In other words, the design of the optical waveguide is seriously restricted by the restriction on the materials, and free design of the optical waveguide is difficult.
The following references are cited to show the state of the art: (i) J. E. Goell, Applied Optics, vol. 12 (1973), page 737; (ii) T. Izawa et al, Applied Physics Letter, vol. 38 (1981), page 483; and (iii) D. H. Hensler et al, Applied Optics, vol. 10 (1971), page 1037.